This invention relates to an apparatus for providing high efficient quenching of roller conveyed glass sheets.
Quenching of heated glass sheets on roller conveyors such as for tempering of heat strengthening is difficult to perform because the conveyor rolls that support the glass sheet for conveyance obstruct the lower glass surface. As such, there is limited area for permitting the jets of quenching gas to impinge with the lower glass sheet surface and for the spent quenching gas to flow downwardly away from the glass sheet after impingement with the glass sheet. Furthermore, the presence of the conveyor rolls below the plane of conveyance provides a different quench configuration than above the plane of conveyance such that the lower and upper glass sheet surfaces are not quenched symmetrically to each other (EP-A-0 114 168).
In order to accommodate for the conveyor roll obstruction problem at the lower glass sheet surface, it is conventional as disclosed in United States patent 4,515,622 McMaster et al to provide quenching gas outlets that are spaced from the glass sheet a distance at least as great as the conveying diameter of the conveyor rolls. Angling of quench tubes through which the quenching gas is supplied as disclosed by the McMaster et al patent permits a greater number of locations of impingement to be provided without blocking the area through which the spent quenching gas flows downwardly away from the conveyed glass sheet after its impingement with the adjacent glass sheet surface.
US-A-4,773,926 discloses apparatus for quenching heat glass sheet in accordance with the preamble of claim 1.
An object of the present invention is to provide improved apparatus for providing high efficient quenching of roller conveyed glass sheets such as for heat strengthening or tempering.
The invention provides apparatus for quenching heat glass sheet in accordance with claim 1.
High efficient quenching of heated glass sheets is achieved by the relative close proximity of the quenching gas outlets to the glass sheet.
In the preferred construction of the apparatus, the outlets are generally round which provides the greatest efficiency in the quenching even through other shapes can be utilized to practice the invention.
In the preferred construction of the apparatus, the upper and lower sets of blastheads of the apparatus are vertically aligned with each other and have the outlets thereof spaced and oriented to provide locations of impingement aligned with each other at the upper and lower surfaces of the conveyed glass sheet. The apparatus also preferably includes a set of upper roll mimics located above the conveyor rolls in a vertically aligned relationship. These roll mimics preferably have W-shaped cross sections. The upper and lower blastheads preferably have the same size and shape as each other so as to thereby cooperate with the conveyor rolls and roll mimics in providing symmetry above and below the plane of conveyance such that the lower and upper glass sheet surfaces are quenched symmetrically to each other.
Best results are achieved when the upper and lower sets of blastheads have the outlets thereof spaced and oriented to provide locations of impingement in an equilateral triangular pattern with the conveyed glass sheets. This equilateral triangular pattern permits the locations of impingements to be as close as possible to each other without obstructing the flow of the spent quenching gas away from the glass sheet after the impingement that provides the quenching.
Each outlet preferably includes a chamfered inlet through which the quenching gas enters the outlet for flow therethrough to the conveyed glass sheet.
The objects, features and advantages of the present invention are readily apparent from the following detailed description of the best mode for carrying out the invention when taken in connection with the accompanying drawings.
With reference to Figure 1 of the drawings, a glass sheet quench system 10 for providing heat strengthening or tempering includes a furnace 10 in which glass sheets G are heated for the quenching and also includes a quench station 14 that embodies apparatus of the present invention for providing quenching of the heated glass sheet as is hereinafter more fully described. Furnace 10 includes a heating chamber 16 in which a roller conveyor 18 is located for providing conveyance of the glass sheet G for the heating in any conventional manner. After heating to a sufficiently high temperature to permit heat strengthening or tempering, the glass sheet G is conveyed from the furnace 12 to the quench station 14 for the quenching. The glass sheet conveyance may be in a single direction from the left toward the right or may be in an oscillating fashion in the furnace 12 and or the quench station 14.
With combined reference to Figures 1 and 2, the apparatus of the quench station 14 includes a roller conveyor 20 having horizontally extending conveyor rolls 22 that convey the heated glass sheet G in a direction of conveyance from the left toward the right along a plane of conveyance C. These conveyor rolls 22 are spaced from each other along the direction of conveyance and have centers 24 about which they rotate to provide the conveyance of the heated glass sheet during the quenching. Each conveyor roll 22 has an outer conveying surface 26 of a round shape with a radius R by a construction that is hereinafter more fully described.
With continuing reference to Figures 1 and 2, the apparatus of the quenching station 14 also includes upper and lower quenches 28 and 30 which include sets of blastheads 32 respectively located above and below the plane of conveyance C. Each blasthead 32 has outlets 34 through which quenching gas is supplied for impingement with the conveyed glass sheet as is hereinafter more fully described. These outlets 34 are each located closer to the conveyed glass sheet G than the conveyor roll radius R.
As shown in Figures 1 through 3 and Figure 7, each blasthead outlet 34 has a hydraulic diameter D and provides a gas flow path having a length L between the outlet and the impingement of the gas flow path thereof with the conveyed glass sheet. More specifically, the hydraulic diameter D is equal to four times the area of the outlet divided by its circumference. Each outlet 34 has a characteristic length of L/D less than 6 which ensures that the gas jets provided are not too diffused before impingement with the glass sheet The outlets are spaced in a pattern as best shown in Figure 3 and oriented as best shown in Figures 2 and 7 to provide the gas flow paths thereof with different angles of incidence at the impingement thereof with the conveyed glass sheet G. Furthermore, the outlets 34 are spaced and oriented to provide impingement locations 36 which, as shown in Figure 4, are spaced at the glass sheet G.
In the preferred construction as illustrated best in Figure 3, the outlets 34 are generally round. This round shape of the outlets provides the greatest efficiency in quenching gas flow so as to thereby provide a more efficient quench station.
As illustrated best in Figure 2, the upper and lower sets of blastheads 32 are vertically aligned with each other and have the outlets 34 thereof spaced and oriented to provide locations of impingement aligned with each other. In other words, each gas flow path impinges with one surface of the glass sheet G at the associated impingement location and another gas flow path impinges with the opposite surface of the glass sheet at the same location so as to provide symmetry in the quenching between the glass sheet surfaces.
As shown in Figure 2, the apparatus also preferably includes a set of upper roll mimics 38 located above the conveyor rolls 22 in a vertically aligned relationship. These roll mimics 38 have a size and shape that mimics the gas flow effect of the conveyor rolls 22 on which the glass sheet is conveyed. Each conveyor roll 22 has a minor diameter and also has its conveyor surface 26 provided by a helically wrapped support 39 provided by woven aromatic polyamide fibers such as sold under the trademark Kevlar E.I. DuPont Company of Wilmington, Delaware, United States of America. Such a support provides conveyance of the glass sheet without marking its heat softened lower surface prior to cooling. Each of the roll mimics 38 has a curved W-shaped cross section as illustrated, but other shapes could also be used so long as the gas flow at the upper glass surface is affected the same as the conveyor rolls affect the quenching gas flow at the lower surface of the glass sheet. The upper and lower blastheads 32 also preferably have the same size and shape as each other in order to provide symmetry in configuration between the upper and lower surfaces of the glass sheet as far as affecting the quenching gas flow. However, it should be understood that the roll mimics 38 do have to be spaced upwardly slightly from the the glass sheet G so as not to engage its upper surface and there is thus not exact symmetry between the upper and lower glass sheet surfaces as far as quenching gas flow is concerned even though such symmetry is substantially approached.
With reference to Figure 4, the lower and upper sets of blastheads have the outlets thereof spaced and oriented to provide the impingement locations 36 in an equilateral triangular pattern with the conveyed glass sheet This equilateral triangular pattern permits the impingement locations 36 to be positioned as close as possible to each other while still maintaining sufficient area for the spent quenching gas to escape after impingement with the glass sheet.
As best illustrated in Figure 7, each blasthead 32 includes a formed sheet metal blasthead member 40 that defines a quench gas plenum 42 and the outlets 34. This formed sheet metal blasthead member 40 is manufactured from flat sheet metal, as shown in Figure 5, through which the outlets 34 are initially stamped with a cylindrical shape. Thereafter, another stamping operation is performed to provide each outlet 34 with a chamfered inlet 44 which may either have sharp bevels as shown or smoothly curved bevels. The sheet metal blasthead member 40 is then formed from the flat condition of Figure 6 to the configuration of Figure 7 such that each outlet 34 has its chamfered inlet 44 through which the quenching gas enters the outlet for flow from the quench gas plenum through the outlet to the conveyed glass sheet. Efficiency is provided in the quenching by this chamfered construction of the inlet 44 of each outlet 34.
As illustrated in Figure 3, each formed sheet metal blasthead member 40 has an elongated shape extending parallel to the conveyor rolls and, as shown in Figure 7, has a formed cross section of a curved shape at which the outlets 34 are located.
As best illustrated by combined reference to Figures 2 and 3, each blasthead 32 has three different sizes of outlets 34 with the smallest outlets having the shortest gas flow path length L and the angle of incidence closest to a perpendicular relationship with the glass sheet plane of conveyance C. On each side of a centerline 46 of each blasthead 32 as illustrated in Figure 2 and 3, the smallest size outlets 34 are located closest to the centerline 46 laterally intermediate the next largest size outlets 34 which have a greater angle of incidence and in alignment with the largest size outlets 34 which have the greatest angle of incidence. Furthermore, the smallest size outlets 34 on each side of the centerline 46 are located laterally intermediate the smallest size outlets 34 on the other side of the centerline 46.
While the best mode for practicing the invention has been described in detail, those familiar with the art to which this invention relates will recognize other embodiments and designs for practicing the invention as defined by the following claims.